The Palaeo-Tethys in East Asia The Phanerozoic evolution of the region involved the opening and closing

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  • CEOSEA '98 Proceeoingd, Ceo L. Soc. MaLaYJia BuLL. 43, December 1999; pp. 131-143

    Ninth Regional Congress on Geology, Mineral and Energy Resources of Southeast Asia - GEOSEA '98

    GEOSEA '98

    17 - 19 August 1998 • Shangri-La Hotel, Kuala Lumpur, Malaysia

    The Palaeo-Tethys in East Asia

    I. METCALFE

    Asia Centre, University of New England Armidale, NSW 2351, Australia.

    Abstract: The main branch of Palaeo-Tethys in East Asia is represented by the Lancangjiang and Changning-Menglian suture zones of western China, the Nan-Uttaradit and Sra Kaeo suture zones of Thailand and the Bentong-Raub suture zone of Peninsular Malaysia. Other subsidiary branches are represented by the Jinshajiang, Ailaoshan and Song Ma suture zones of western China and Vietnam and the Qinling-Dabei suture zone of north and central China. A further possible Palaeo-Tethyan suture zone segment has also been recognised in southern Guangxi, south China. New data from the Palaeo- Tethys remnants along these sutures, particularly in Yunnan, Thailand and Malaysia, suggest that the Palaeo-Tethys opened in the Devonian when the first of three continental slivers (comprising North China, South China, Tarim, Indochina and Hainan) rifted and separated from northern Gondwanaland. The branch of Palaeo-Tethys which separated South China and Indochina closed by Early Carboniferous times in its eastern part along the Song Ma suture, but much later in the west along the Ailaoshan suture during the Triassic. Radiolarian biostratigraphic and other data suggest that the main Palaeo-Tethys was closed when the Sibumasu-Qiangtang terranes amalgamated with Indochina/South China in the Permian-Triassic.

    INTRODUCTION

    East Asia is a composite of allochthonous continental terranes whose boundaries are marked by major fault zones or by sutures recognised by the presence of ophiolites, melanges and accretionary complexes (Fig. 1). Stratigraphical, sedimentological, palaeo biogeographical and palaeomagnetic data suggest that all of the East Asian continental terranes were derived directly or indirectly from northeast Gondwanaland. The Palaeozoic to Cenozoic evolution of East and Southeast Asia is essentially one of rifting of terranes from the northeastern margin of Gondwanaland, their northwards migration and amalgamation to form present day Asia.

    The Phanerozoic evolution of the region involved the opening and closing of three successive ocean basins, the Palaeo-Tethys, Meso-Tethys and Ceno- Tethys (Metcalfe, 1990, 1996a, 1996b, 1998). These ocean basins opened as a consequence ofthe rifting, separation, and northwards drift of three elongate continental slivers from the margin of Gondwanaland (Fig. 2). The Palaeo-Tethys ocean basin opened in the Devonian when the first continental sliver, comprising North China, South China, Tarim and Indochina, separated from the Gondwanaland craton. The Meso-Tethys ocean opened in the late Early to Middle Permian when

    the second continental sliver, compnsmg the Sibumasu block, Qiangtang block and other elements of the Cimmerian continent, separated from the margin of Gondwanaland.

    The Ceno-Tethys ocean basin opened behind the third continental sliver (Lhasa block, West Burma, and other small continental fragments now located in SW Sumatra, Borneo and Sulawesi) in the Late Triassic-Late Jurassic. Amalgamation and accretion of the terranes derived from the margin of Gondwanaland took place progressively during Carboniferous to Cenozoic times, terranes essentially nucleating around South China and then accreting to Eurasia.

    THE PALAEO-TETHYS IN EAST AND SOUTHEAST ASIA

    Remnants of the Palaeo-Tethys ocean are preserved within a number of suture zones that separate allochthonous continental terranes in East Asia. The main Palaeo-Tethys ocean is represented by the Lancangjiang and Changning-Menglian sutures in Tibet and Yunnan, and the Nan- Uttaradit-Sra Kaeo and Bentong-Raub sutures in Thailand and Malaysia respectively (Fig. 1). To the west of these sutures, terranes exhibit Gondwanaland faunas and floras and marginal Gondwanaland stratigraphies up until the Lower

  • 132 I. METCALFE

    NORTHEAST CHINA {COMPOSITE

    PALAEO-TETHYS Main Branch

    - - • Other Branches

    D Terranes derived from Gondwanaland in the Devonian

    mIIIIIIIIJ Terranes derived from Cathaysia land in the Cretaceous-Tertiary

    NORTH CHINA

    BENGKULU

    - Terranes derived from Gondwanaland in the late Early Permian D Indian continent derived . . from Gondwanaland in the Cretaceous

    0 '-0 ® @ ® ® 0 ® ® @ ® ® @ @ ® ® ® ® ®

    - ~

    Song Ma

    Aibi-Xingxing

    Xiliao-He

    Kunlun

    Qinling-Dabie

    Jinshajiang

    Lancangjiang

    Banggong

    Indus Yarlung Zangbo

    Nan-Uttaradit

    Bentong-Raub

    Shan Boundary

    Woyla

    Meratus

    Boyan

    Changning-Menglian

    Ailaoshan

    Sra Kaeo

    Southern Guangxi

    Terranes derived from Gondwanaland in the Late Triassic-Late Jurassic

    Songpan Ganzi accretionary complex

    Figure 1. Distribution of principal continental terranes and Palaeo-Tethyan and other sutures of East and Southeast Asia. WB = West Burma, SWB = South West Borneo, S = Semitau Ten-ane, HT = Hainan Island terranes, L = Lhasa Terrane, QT = Qiangtang Terrane, QS = Qamdo-Simao Terrane, SI= Simao Terrane, SG = Songpan Ganzi accretionary complex, KL = Kunlun Terrane, QD = Qaidam Terrane, AL = Ala Shan Ten-ane, KT = Kurosegawa Terrane.

    GEOSEA '98 ProceedlngJ (GSM BIlLL. 43)

  • THE PALAEO-TETHYS IN EAST ASIA 133

    Permian (Stauffer and Mantajit, 1981; Archbold et . ai., 1982; Waterhouse, 1982; Burrett and Stait, 1985; Metcalfe, 1986, 1988, 1990, 1991, 1992, 1993; Rao, 1988; Stauffer and Lee, 1989; Burrett et ai., 1990; Fang and Yang, 1991; Shi and Waterhouse, . 1991; Jin, 1994a, 1994b; Racey et ai ., 1994; Wopfner, 1994; Archbold and Shi, 1996; Yang, 1996). To the east, the terranes exhibit Lower Palaeozoic Gondwanaland faunas but Tethyan/Cathaysian Late Palaeozoic faunas and floras and show no evidence of post-Devonian Gondwanaland biogeographic affinities or related stratigraphy (Metcalfe, 1986, 1988). Other branches of the Palaeo-Tethys are represented by the Ailaoshan suture in Yunnan, the Song 'Ma suture in North

    Vietnam and by possible Palaeo-Tethyan suture zone segments in North Thailand and Southern Guangxi, Chiha (Fig, 1).

    New data from the Palaeo-Tethys remnants along these sutures, particularly in Yunnan, Thailand and Malaysia (see below), suggest that the Palaeo-Tethys opened in the Devonian when the first of three continental slivers (comprising North China, South China, Tarim, Indochina and Hainan) rifted and separated from northern Gondwanaland. The branch of Palaeo-Tethys which separated South China and Indochina · closed by Early Carboniferous times in its eastern part along the Song Ma suture, but much later in the west along the Ailaoshan suture during the Triassic.

    COLLISION (AMALGAMATION & ACCRETION)

    SEPARATION

    Late Devonian

    Early Permian

    Late Triassic

    Late Jurassic

    Late Triassic

    Early Cretaceous

    Eocene

    Figure 2. Schematic diagram showing the three continental slivers/collages of terranes, rifted from Gondwanaland and translated northwards by the opening and closing ofthree successive oceans, the Palaeo-Tethys, Meso-Tethys and Ceno-Tethys,

    December 1999

  • 134 I. METCALFE

    Radiolarian biostratigraphic and other data suggest that the main Palaeo-Tethys was closed when the Sibumasu-Qiangtang terranes amalgamated with Indochina/South China in the Permian-Triassic.

    Yunnan and Tibet, China The Palaeo-Tethys in Yunnan and Tibet is

    represented by the main Palaeo-Tethyan Lancangjian and Changning-Menglian suture zones and by the Jinshajiang and Ailaoshan suture zones that represent subsidiary branches of the Palaeo- Tethys (Fig. 3). Recent biostratigraphic studies have revealed the presence of oceanic ribbon-bedded chert-shale sequences that have yielded graptolites, conodonts and radiolarians indicating ages ranging from Lower Devonian to Upper Triassic in the Changning-Menglian suture, Upper Devonian to Middle Triassic in the Jinshajiang suture and Lower Carboniferous to Lower Permian in the Ailaoshan suture (Qin et al., 1980; Duan et al., 1982; Wu and Zhang, 1987; Wu and Li, 1989; Liu et al., 1991, 1996; Feng and Liu, 1992; Feng and Ye, 1996; see Fig. 4). Other constraining data (Table 1) indicates that the Palaeo-Tethys opened in the Devonian and that the Lancangjiang and Changning-Menglian segments of the main Palaeo-Tethys, and the Jinshajiang subsidiary branch closed in the Late Triassic and that the Ailaoshan branch closed a little earlier in the Middle Triassic.

    Thailand The Palaeo-Tethys is represented in Thailand

    by the N an-Uttaradit and Sra Kaeo suture segments (Fig. 5). These suture zone segments contain pre- Permian ophiolites, melange and accretionary complex material of Carboniferous to Middle Triassic age (see Metcalfe, 1996a; and Table 1) and oceanic bedded cherts of Late Devonian? and Carboniferous to Middle Triassic ages (Caridroit et al., 1990; Caridroit, 1991, 1993; Caridroit et al., 1992; Sashida et al., 1993; Fig. 4). Data from the suture zones indicate that the Thailand segments of the Palaeo-Tethys opened in the Devonian and closed in the Late Triassic.

    Peninsular Malaysia The